1. Field of the Invention
The present invention relates to an ink jet ink, and an ink cartridge and an ink jet recording method using such an ink, and a polymer particle used in such an ink.
2. Description of the Related Art
An ink containing a polymer particle has been investigated for the purpose of improving fastness properties of an image. Emulsion polymerization in water is general as a process for synthesizing the polymer particle. Upon emulsion polymerization, it is necessary to use an emulsifier for stably dispersing (emulsifying) a hydrophobic monomer in water. A surfactant is generally used as the emulsifier. The surfactant works for incorporating the hydrophobic monomer in a micelle formed to stably disperse the monomer in water. Upon emulsion polymerization, the surfactant is used in an amount more than a critical micelle concentration for always stably retaining emulsion in a polymerization system. Therefore, a surfactant contributing to no polymerization and a surfactant separated from the polymer particle obtained by the emulsion polymerization are present to no small extent in an ink containing the polymer particle obtained by the emulsion polymerization. When the surfactant remains in the ink in such a manner, a phenomenon that a bubble generated in a liquid becomes hard to disappear (a phenomenon that defoaming properties are lowered) occurs. This is considered to be caused by the remaining surfactant. When such an ink low in defoaming properties is ejected from a recording head of an ink jet system, the viscosity of the ink is increased by the influence of a bubble generated in the ink to lower the ejection stability of the ink.
In order to improve the defoaming properties of an ink, a polymer particle obtained by emulsion polymerization using a surfactant high in defoaming properties has thus been investigated (Japanese Patent Application Laid-Open No. H09-267034). Japanese Patent Application Laid-Open No. H09-267034 discloses that a polymer particles improved in defoaming properties is obtained by emulsion polymerization using a specific nonionic polymer surfactant as the surfactant high in defoaming properties.
On the other hand, a polymer particle of a core-shell structure is used in a field of an ink jet ink (Japanese Patent Application Laid-Open No. 2011-026553 and Japanese Patent Application Laid-Open No. 2011-011449). Japanese Patent Application Laid-Open No. 2011-026553 and Japanese Patent Application Laid-Open No. 2011-011449 describe an ink containing a polymer particle of a core-shell structure in which a core is formed of a hydrophobic polymer, and a shell is formed of a polymer having an ionic hydrophilic group.